**Core Concept**
In the GOBI (Growth monitoring, Oral rehydration, Breastfeeding, Immunization) initiative, each letter represents a key component of infant and child care. The GOBI initiative aims to improve child survival and development in developing countries. The correct answer will reveal a critical aspect of child health.

**Why the Correct Answer is Right**
The correct option represents the 'Breastfeeding' component, which is crucial for infant nutrition, growth, and development. Breast milk provides essential nutrients, antibodies, and hormones that support the infant's immune system and overall health. The World Health Organization recommends exclusive breastfeeding for the first six months of life.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because growth monitoring is an essential component of child health, but it is not the 'O' in GOBI.
**Option B:** Oral rehydration is a vital component of child health, but it is represented by the 'O' in ORS (Oral Rehydration Solution), not GOBI.
**Option C:** Immunization is a critical component of child health, but it is represented by the 'I' in GOBI, not the 'O'.

**Clinical Pearl / High-Yield Fact**
Remember that exclusive breastfeeding for the first six months of life reduces the risk of infant mortality, diarrhea, and respiratory infections.

**Correct Answer:** D. Breastfeeding.